If you want to make an omelet, you’ve got to break a few eggs: demolishing the old Willamette River Bridge

Although ODOT officially closed the Interstate 5 Willamette River Bridge in 2004, it has towered above the Willamette River between Eugene and Springfield for the past five years, a 60-foot-tall reminder of the hard work to come on the OTIA III bridge program’s largest single bridge replacement project to date.

After years of planning, the dirty work has begun, as ODOT’s contractors demolish the existing structures and build a pair of new, graceful deck-arch bridges in their place.

The demolition process draws oohs and aahs from spectators, as massive prehistoric-looking munchers and crunchers systematically dismantle the thousands of yards of concrete, then separate the steel, cement and asphalt for disposal, reuse or recycling.
In the months leading up to the beginning of demolition, ODOT’s teams worked almost around the clock to be sure the bridge would come down on time, without a hitch and with minimal disruption to the natural environment around it.

The work bridge

Photo courtesy of Hamilton Construction
The first step in the demolition process is creating a foundation to support the people and machines that will deconstruct the bridge. For this project, the team built a platform spanning the entire river and standing about 10 feet above the high-water mark. The platform not only gives the demolition crew access to the bridge, it also acts as a catchall for debris, which in turn helps keep the river beneath it clean and undisturbed.

On a project of this scale everything is big, and the work bridge is no exception. At approximately 120,000 square feet, this structure—composed mainly of steel and massive wood timbers—has a footprint as big as some Costco stores.

The work bridge stands on 263 steel pilings driven into the riverbed. To comply with Oregon Department of Fish and Wildlife in-water work windows, the construction team had to build the work bridge in a tightly constrained time period: less than three months.

In-water work

Photo by Gary Weber, ODOT Photo and Video Services

Working above and in the Willamette River requires careful planning, close monitoring and flawless execution to ensure the bridge replacement project has minimal impact on the surrounding natural areas.

The massive demolition containment structure and work bridge are supported by large steel piles. For this project, crews used hammers that run on canola oil, an all-natural vegetable oil to pound the piles into the riverbed. Once this portion of the project is completed, the team will remove the entire work bridge and reuse it on the second stage of the project: removing the detour bridge.

In addition to working within carefully prescribed work periods to reduce any effects on local fish populations, the project team deployed a custom-built tool known as the “Bubbleator,” pictured above. This structure, which a large crane places where each pile is driven, provides the team with numerous advantages, including a safe work platform, a sturdy frame, and environmental benefits that are more obvious from below the water’s surface.

The name Bubbleator refers to the curtain of air bubbles the tool releases when engaged. Those bubbles, combined with the thick walls of the Bubbleator, dampen sound, significantly reducing the impacts of pile driving on the fish and other native species living underwater near the bridge project area.
And the bridge comes down

Photo by Gary Weber, ODOT Photo and Video Services
Once the demolition containment efforts are complete, massive excavators roll onto the work platform and begin the methodical process of disassembling the bridge. The grey and red Link Belt 210 machines tip the scales at 46,000 pounds each. They can be equipped with a variety of demolition tools including demolition hammers—a gargantuan jackhammer—or hydraulic shears that are capable of cutting through massive sections of steel-reinforced concrete with ease.

Usually, a bridge demolition like this would occur from both the top and bottom. Careful engineering in the months leading up to the demolition helps determine the bridge’s capacities and ensures the structure will be able to support heavy machinery as the demolition progresses. However, once crews opened up the bridge, they discovered unexpected conditions that forced them to alter the original plans. Because of certain construction methods, the bridge would not have been able to safely support excavators demolishing it from its surface.

To address the weight restriction problem, the project team brought in a pair of bright yellow 400-class Komatsu high-reach excavators. These mega-machines, weighing in at more than 100,000 pounds each, have custom-built arms that enable them to reach 70 feet into the air and work with any of the standard attachments to provide munching and crunching power all the way up to the top of the bridge deck.
Recycling and reuse

Photo by Gary Weber ODOT Photo and Video Services

Once demolition begins, the excavators work nearly constantly, devouring large bridge sections one at a time. This carefully coordinated process is designed to allow the operating engineers to safely pull the bridge onto the deck, where large pieces are broken down into smaller rubble and materials are separated for reuse and recycling.

The steel—stripped of almost all concrete—is grouped into long bundles or compact balls by massive exactors, whose nimbleness appears at odds with their size and destructive abilities. Some of the smashed concrete is hauled away for direct reuse as fill material; some is crushed even smaller and recycled into new concrete. In the end, the bridge will yield approximately 30 million pounds of debris, most of which will be reused or recycled.

In this photo, the excavators are working on a large pile of steel and concrete, all that is left from the gap above them where a highway bridge formerly stood for half a century.
The big lift

Photo courtesy of Hamilton Construction
Crews demolished the decommissioned bridge over the river to the level of the work bridge in less than two months. However, a big part of the project remained for the team, both literally and figuratively. Five remaining bridge piers weighed more than 200,000 pounds and sat below the level of the work bridge, mostly submerged in the river.

To remove the piers, the demolition crew used a diamond-impregnated wire saw—a thin, ultra-sharp blade that wraps around the base of the pier—to cut the piers off flush with the riverbed. Heavy-duty cranes then attach to the piers, via bolts inserted through three-inch diameter holes, and lift all 110,000 tons of pier onto the bridge deck to be broken down by the exactor, equipped with the demolition hammer in the photo above.

This process is a vast improvement over earlier demolition methods, which required building an extensive cofferdam to reroute the river, then demolishing the structure on the riverbed’s mud.
What’s next?

Photo courtesy of Hamilton Construction
In a matter of weeks, the structure that had allowed I-5 motorists to cross the Willamette River for half a century was torn down, reduced to rubble and hauled away. Most of the materials will be reused, and parts of the original bridge will see a new life in roads, bridges or buildings around the region in the near future.

The demolition of the bridge is only the first of many steps in this giant bridge replacement. In the coming weeks, crews will demolish other parts of the bridge, including the section on the south end, which crosses the railroad tracks.

Even as this initial process draws to a close, project team members are already hard at work on the next step of the project. In a couple of years, they will move the work bridge and repeat the demolition process on the current detour structure. In the near future, the team will start building the foundation for the arch ribs, the sole point where the new bridge’s gracefully curving arches will touch down in the river.